docs: def _validate_fetch(self):
          """Validate the fetch.txt file
  
          Raises `BagError` for errors and otherwise returns no value
          """
          for url, file_size, filename in self.fetch_entries():
              # fetch_entries will raise a BagError for unsafe filenames
              # so at this point we will check only that the URL is minimally
              # well formed:
              parsed_url = urlparse(url)
  
              # only check for a scheme component since per the spec the URL field is actually a URI per
              # RFC3986 (https://tools.ietf.org/html/rfc3986)
              if not all(parsed_url.scheme):
                  raise BagError(_('Malformed URL in fetch.txt: %s') % url)